Supported catalysts, in particular supported metal or metal oxide catalysts, are well known in the art. Dispersions of small metal particles on metal oxide substrates are commonly used as catalytic materials. The physical and chemical properties of the final catalyst can depend strongly on the preparation of the substrate prior to deposition of the metal particles, on the methods of deposition used and on any subsequent treatments of the metal/oxide system.
The ability to prepare high loaded metal catalysts that have small particle sizes (high dispersion) and metal particles that are homogeneously distributed on the support surface is an important requirement for effective supported catalysts. In many instances, particularly with base metal catalysts, highly loaded metal catalysts have large metal particles (>10 nm) that are clustered in localized areas on the support. Since catalytic activity of many reactions correlates with the number of available surface metal sites, it is important to be able to produce catalysts with good metal dispersion. Uniformity of the distribution of catalytic metal sites is also an important factor and maximization of the inter-particle distance can help to provide for stable supported catalysts with reduced sintering problems. Supported metal catalysts are often prepared by incipient wetness impregnation of solutions containing metal salts, dried and then calcined to form the oxides. The oxides are then reduced to form the supported metal catalysts.
There have been various attempts in the art to improve the dispersion of active metals deposited on refractory inorganic oxide supports to produce catalysts for use in Fischer-Tropsch processes. In particular there have been various approaches adopted in the art to reduce the amount or rhenium or other group 8 metals required in combination with the catalytic metal.
In published International Patent Application No. WO 98/47618, multifunctional carboxylic acids having from about 3 to 6 total carbon atoms are co-deposited with sources of catalytically active metal onto a refractory metal oxide followed by calcination to prepare Fischer-Tropsch catalysts. Examples of the multifunctional carboxylic acids include various amino acids.
In published International Patent Application No. WO 98/47620, carbohydrate or sugars are either co-deposited with sources of catalytically active metal or are applied after deposition of the source of catalytically active metal onto a refractory metal oxide followed by calcination to prepare Fischer-Tropsch catalysts.
In published International Patent Application No. WO 98/47617, polyols are co-deposited with sources of catalytically active metal onto a refractory metal oxide followed by calcination to prepare Fischer-Tropsch catalysts.
There is a continuing need for new methods for the preparation of supported metal catalysts, which enable the dispersion of metal in the final catalyst to be controlled.
It is therefore an object of the present invention to provide processes for the manufacture of supported metal catalysts, which enables the control of metal dispersion in the catalyst.